The invention relates to a mold-closing unit for an injection molding machine to process plastics materials and other plasticizable masses such as powdery or ceramic masses in accordance with the preamble of claim 1, this mold-closing unit having a mold height adjustment device.
By xe2x80x9cmold heightxe2x80x9d is here understood the height of the mold which is measured in the closing direction and which corresponds to the distance between the moveable mold carrier and the stationary mold carrier when the mold is closed. Adjusting devices of this kind are first of all necessary in injection molding machines in which the closing movement and the building-up of the locking pressure takes place via a toggle joint, since the support plate for the toggle joint has to be positioned in relation to the integrated injection molding tool in such a way that as the too or the mold is closed, the toggle joint is expanded and thus can apply is maximum locking pressure in each cycle.
From PATENT ABSTRACTS OF JAPAN, vol. 16, No. 471 (M-1318), 1992-09-30) and JP 04 169216 A is known a mold-closing unit, underlying the preamble of claim 1 and having a mold height adjustment. This mold height adjustment is used as usual in connection with a toggle joint as the closing mechanism. On the moveable mold carrier, an electromagnetically actuatable fixing device is provided and on the support element for the toggle joint mechanism a fixing device is provided which may be actuated manually to detachably fix the support element. If when the moveable mold carrier is fixed and the support element detached, the closing motor driving the toggle joint is actuated, the support element is displaced into the necessary position for the new mold height, in which the locking pressure can be applied with the toggle joint in an expanded position. The support element is not fixed in a positive manner, and thus after a plurality of cycles at least the precision suffers in the repeated application of the locking pressure. Above all however this mold height adjustment has no influence on the opening path to open the mold, since this is dependent on the movement of the toggle joint and not on the position of the support element.
Mold-closing units with mold height adjustments are known in which there are provided on bars, which are mostly fixed to the stationary mold carrier and serve to guide the moveable mold carrier, threaded portions which are connected with nuts. These nuts are driven via a separate drive to adjust the mold height. The nuts have on their outer side a ring gear, such that they can be actuated either with a ring gear or with a toothed belt. (U.S. Pat. No. 4,281,977; Brochure xe2x80x9cElektra S-Seriexe2x80x9d (p.5) of the company Ferromatic Milacron Maschinenbau GmbH, 79364 Malterdingen).
For adjusting the mold height and locking a support plate for the closing mechanism, the company Engel Vertriebs GmbH, A-4311 Schwertberg, Austria has a known way of providing the bars with grooves and fixing to these grooves two half nuts by moving the half-nuts in a radial direction towards one another until they come into contact with the grooved region of the guide bars.
Furthermore, from the company Husky Injection Molding Systems there is a known way of achieving locking of this kind with a bayonet fastening. For this purpose, the bar has regions into which a closing piston can engage, as well as regions along which the moveable dosing piston can slide radially on the guide bars. By turning the closing piston, a positive-locking effect is caused, such that at least a portion of the locking pressure can also be applied to this piston simultaneously. This use is not however for adjusting the mold height but, as in DE 42 43 735 C, to fix the moveable mold carrier in a two-plate system, without any influence being exerted on the closing drive.
From DE 24 29 570 B1 is known an injection molding machine in which two pressure cylinders are used to close the mold. One pressure cylinder serves to displace the moveable mold plate, a further cylinder to apply the locking pressure. Correspondingly, even during the injection molding cycles, two plates are moved jointly as the moveable mold carrier. A support element which is adjustable with an alteration of the mold height is not provided. The fixing device is only actuated when the piston of the cylinder has completed its stroke movement and in addition now the locking pressure is to be applied via the piston.
From DE 49 43 735 C2 is known a two-plate machine in which, in order to achieve the mold closure, the moveable mold plate is drawn towards the stationary mold carrier. The moveable mold carrier is separable from the guide bars which are necessary during the application of the locking pressure and can be locked to same. However once the locking has been accomplished, it is only the closing cylinder which is responsible for the mold closing movement and the application of the locking force. Alteration and thus optimization of the locking pressure is thus not possible.
In parallel proceedings, the document DE 30 42 712 was cited, the object of which is completely different however, since there, on engagement grooves of the guide bars, a locking mechanism for the protective bolt is triggered and locked, which covers the mold tentering space.
Proceeding from this prior art, the object underlying the present invention is to create a mold-closing unit of the type mentioned initially in which the height adjustment can be used simultaneously to optimize the opening stroke.
This object is achieved by a mold-closing unit with the features of claim 1.
Associated with the moveable mold carrier is a fixing device, such that the moveable mold carrier can be fixed in any way in its current position. If the locking of the drive is detached from the bars, the drive can be adjusted with its respective support relative to the bars, such that a mold height adjustment occurs. Since the drive device usually used for a main axis can now be used for a subordinate function, an additional drive for the adjustment of the mold height can be dispensed with. Additional guide elements are not necessary since the guide elements which are present anyway, generally the tie bars, can be used. In contrast to the previously-known mold height adjustments on toggle joint closing mechanisms, independently of the mold height on closing mechanisms with linear movement means, the opening stroke or the closing path can be simultaneously optimized, when injection molds of differing heights are used on one and the same machine. Since, as a result of their purely linear movement, these units are adjustable in any way in respect of the opening stroke, providing such mold-closing units with a height adjustment system was previously refrained from. Through the use of the mold height adjustment device, however, in each cycle the pressure build-up times can be reduced in the order of several tenths of seconds. There is thus an optimization of the position of the whole closing unit.